Digital communication receivers often sample an analog waveform and then reliably detect the sampled data. Signals arriving at a receiver are typically corrupted by intersymbol interference (ISI), crosstalk, echo, and other noise. In order to compensate for such channel distortions, communication systems often employ well-known pre-emphasis techniques in the transmitter or equalization techniques in the receiver (or both). On the receiver side, well-known zero equalization or decision-feedback equalization (DFE) techniques (or both) are often employed.
A communication channel typically exhibits a low pass effect on a transmitted signal. Conventional pre-emphasis employed by a transmitter attempt to open the received data eye that has been band limited by the low pass channel response. Thus, the channel will generally impair the higher frequency components of a transmitted signal more than the lower frequency components. While existing pre-emphasis techniques effectively compensate for channel distortions, they suffer from a number of limitations, which if overcome, could further improve the reliability of data detection in the presence of channel distortions.
A need exists for improved pre-emphasis techniques that amplify the high frequency content of transmitted data. A further need exists for methods and apparatus for applying increased pre-emphasis to higher frequency components of a transmitted signal, such as clock-like data patterns.